Except we have no evidence to support the idea of being "transracial."
With people who are trans we can crack their skull open to find a brain that more resembles the sex the individual identifies as.
Crack their skull open? I'm sure you didn't mean it literally, but it's just a weird image that popped into my head.
I'm not sure what "transracial" would even imply. I do know of situations where someone of one race who, by adoption or circumstance, happened to be raised among people of another race. I knew a woman who was born in Korea, but adopted as a baby by white American parents, so linguistically and culturally, she was more American than Korean. But she didn't make any attempt change her external features, as that would be kind of weird.
I don't think that people need to make any physical changes to their appearance, but I can understand if people spend enough time in a community, they'll adopt some of the ways and culture of the community and begin to identify with it. If it's a mixed community where there are multiple cultures living in close proximity, they rub off on each other and influence each other.
I suppose it's possible for people to lose sight of reality and get confused. A white person might actually think that she's black, but I'm not sure I would read any malicious intention in that. Such a person might genuinely be mentally ill. However, if someone does it for political opportunism or some other nefarious purpose, then that would be different.